1. Field of the Invention
This invention relates generally to wireless telecommunication. More particularly, it relates to Voice Over Internet Protocol (VoIP) E9-1-1 call flows supporting unlicensed mobile access (UMA).
2. Background of the Related Art
Unlicensed Mobile Access (UMA) is the Third Generation Partnership (3GPP) standard for cellular and wireless fidelity (WiFi) convergence. The UMA specifications are publicly available, e.g., from the UMA Technology web site (www.umatechnology.org) as well as from the 3GPP web site (www.3gpp.org).
The UMA effort was initiated by leading operators and vendors in the wireless industry, with a goal of developing a set of technical specifications for extending mobile voice, data and IP Multimedia Subsystem (IMS) services over broadband IP and Wi-Fi access networks. On Apr. 8, 2005, the specifications were officially incorporated into 3GPP Release 6, making UMA the true global standard for cellular/Wi-Fi convergence. The UMA effort has been a tremendous success, having developed a new global communications standard in a period of less than 15 months.
For mobile operators, Wi-Fi had been viewed as somewhat of a threat. Now, UMA provides a secure, managed IP connection established between a mobile handset and the operator's core network. Thus all of an operator's mobile services (voice, data, and IMS) are available to the subscriber when connected via Wi-Fi. In addition, with UMA, active voice calls and data sessions are automatically handed over between networks as subscribers come in and out of range of WLANs. Thus, with the use of UMA, Wi-Fi no longer poses a threat to mobile operators because they maintain control of their subscribers and services even when connected via Wi-Fi.
The current UMA E9-1-1 standard calls for E9-1-1 calls NOT to be processed over the IP network but instead to be transitioned to a GSM TDM call flow. However, the present inventors have realized that this is a problem because of the high potential for such a transitioned E9-1-1 call to be dropped. Needless to say, a significant number of dropped emergency calls are problematic and the source of potential liabilities to an operator.
Some GSM carriers have followed different implementations of the UMA E9-1-1 call flow. For instance, at least one carrier (e.g., T-Mobile™) has implemented an approach utilizing a serving mobile location center (SMLC). Unfortunately, disadvantages with such conventional solutions include the fact that switching E9-1-1 calls back to a time division multiplexed (TDM) system may cause those calls to drop in houses having poor cellular coverage.
There is a need for a more reliable handling of emergency calls that use UMA.